1. Field of the Invention
The present invention relates to MUTs and, more particularly, to a MUT circuit with an electrically controllable membrane.
2. Description of the Related Art
A transducer is a device that converts an electrical signal into a type of energy, such as acoustic energy, and converts the type of energy, such as the acoustic energy, into an electrical signal. A micromachined ultrasonic transducer (MUT) is a micromachined transducer that converts an electrical signal into a transmitted ultrasonic wave, and converts a received ultrasonic wave into an electrical signal.
The basic component of a MUT is a suspended membrane or diaphragm which is capable of vibrating. When the membrane vibrates due to electrical stimulation, the membrane outputs ultrasonic waves. On the other hand, when the membrane vibrates due to an incoming ultrasonic wave, the movement of the membrane generates an electrical signal or a change in a measurable electrical property of the device. Two common types of MUTs are a capacitive MUT (CMUT), and a piezoelectric MUT (PMUT).
FIG. 1 shows a schematic diagram that illustrates an example of a MUT circuit 100 in accordance with the present invention. As shown in FIG. 1, MUT circuit 100 includes a MUT 110, which has a MUT membrane 112 that can vibrate back and forth in a down direction D1 to a down position P1, and in an up direction D2 opposite to the down direction D1 to an up position P2. MUT 110 can be implemented with any MUT, such as a CMUT or a PMUT.
As further shown in FIG. 1, MUT circuit 100 includes a transmit circuit 114, a receive circuit 116, and a digital signal processing circuit 118. Transmit circuit 114 and receive circuit 116 are both electrically connected to MUT membrane 112, while digital signal processing circuit 118 is electrically connected to receive circuit 116.
For example, transmit circuit 114 can be implemented with a pulse generator 120 that is electrically connected to MUT membrane 112, and a controller 122 that is electrically connected to pulse generator 120. Receive circuit 116, in turn, can be implemented with an amplifier/filter circuit 124, and an analog-to-digital (A/D) converter 126 that is electrically connected to amplifier/filter circuit 124 and digital signal processing circuit 118.
In operation, when MUT circuit 100 transmits, controller 122 commands pulse generator 120 to output a voltage pulse VP to MUT membrane 112. The voltage pulse VP, in turn, causes MUT membrane 112 to vibrate at the natural mechanical resonant frequency of MUT 110, and thereby generate an ultrasonic wave UW at that frequency.
FIGS. 2A-2B are timing diagrams that illustrate an example of the transmission operation of MUT circuit 100 in accordance with the present invention. FIG. 2A shows a timing diagram that illustrates a voltage pulse VP, while FIG. 2B shows a timing diagram that illustrates an example of an ultrasonic wave UW that is generated by MUT 110 in response to the voltage pulse VP. The x-axis represents time in FIG. 2A, while the y-axis represents voltage amplitude. The x-axis represents an at-rest position of MUT membrane 112 in FIG. 2B, while the y-axis represents the acoustic amplitude or the physical movement of MUT membrane 112.
As shown in FIG. 2A, when MUT circuit 100 transmits, a voltage pulse VP causes MUT membrane 112 to vibrate and generate an ultrasonic wave UV at the natural mechanical resonant frequency of MUT 110. In addition, as further shown in FIG. 2B, the amplitude of each ultrasonic wave UW decays over time based on the physical dampening mechanism of MUT 110, and substantially goes to zero before the next voltage pulse VP occurs.
When MUT circuit 100 receives, an incoming ultrasonic wave causes MUT membrane 112 to vibrate. The vibration of MUT membrane 112 generates an electrical signal or a change in a measurable electrical property of the device that causes an output voltage to vary. Amplifier/filter circuit 124 amplifies and filters the varying output voltage, while A/D converter 126 generates a digitized signal that represents the varying output voltage. The digitized signal is then processed by digital signal processing circuit 118 as required by the application to generate, for example, an ultrasonic image or a simple distance measurement.
Although MUT circuit 100 works well for numerous applications, such as contact or near contact body imaging applications like echo cardiograms, MUT circuit 100 lacks sufficient bandwidth for some airborne applications. Thus, there is a need for a MUT circuit which can operate in those airborne applications that require a larger bandwidth.